Aligning exposure method

ABSTRACT

Disclosed .[.in.]. .Iadd.is .Iaddend.an aligning and exposing method suitable for use in the production of LSIs. Coherent ray beams are applied from two directions to form .Iadd.an .Iaddend.interference fringe through interference of the coherent rays. A diffraction grid is disposed in the optic paths of the ray beams substantially in parallel with the interference fringe. The ray beams reflected .[.and.]. .Iadd.or .Iaddend.transmitted by the grid are converged by a lens system and the intensities of the ray beams are measured to detect the relative position between the interference fringe formed by two coherent ray beams and the diffraction grid, thereby to permit a highly accurate alignment of fine semiconductor element. The pitch of the grid on the substrate is selected to be n (n being an integer) times as large as the pitch of the interference fringe, so that the grid for alignment purpose is formed simultaneously with the formation of the LSI pattern by photolithographic technic. With this method, it is possible to attain a high degree of accuracy of alignment, and to conduct the subsequent exposure using the same ray beam source as that used for the alignment.

BACKGROUND OF THE INVENTION

The present invention relates to an aligning method which ensures a highprecision of alignment and which is suited to the aligning apparatus forproducing .Iadd.a .Iaddend.large-scale integrated semiconductor device(referred to as "LSI", hereinunder). The invention is concerned alsowith an exposure method for making a transfer of a pattern by thealigning method mentioned above.

FIGS. 1a and 1b show an example of conventional aligning methods. Morespecifically, FIG. 1a shows an example of an aligning pattern on a photomask. In this example, a transfer pattern α1 for the aligning pattern isformed on a wafer by means of radial lines of a constant line width,while FIG. 1b shows how a further alignment is made on the aligningpattern formed on the wafer with the same pattern. Namely, the shadow α2of an aligning mark formed on a photo mask is aligned with the patternα1 formed already on the wafer. This aligning method can provide adegree of aligning precision on the order of ±0.3 μm which is quiteunacceptable for the alignment of LSI having a gate length of less than1 micron. In fact, LSIs of 0.5 micron rule require a high degree ofaligning precision of 0.05 μm which can never be achieved by theconventional aligning method.

Austin et al proposes, in Applied Physics Letters Vol. 31, No. 7, p.428, 1977, an aligning method making use of a double grid. In thismethod, as shown in FIG. 2, an incoming laser beam is applied to a photomask 2 and is diffracted by a grid 3 formed on the photo mask 2. Thediffracted ray is diffracted once again by a grid 5 formed on the wafer4 to obtain diffracted ray beans 6, 7, 8 . . . These diffracted raybeams 6, 7 and 8 can be expressed as (0, 1), (1, 1), (-1,2) . . . bybinary representation in terms of the order of diffraction on the photomask and the order of diffraction on the wafer. These diffracted beamsare focussed on a point by means of a lens for the measurement of theray intensity. The diffracted ray beam has a ray intensity distributionin bilateral symmetry with respect to the incoming laser beam 1, so thatthe alignment of the photomask 2 with the wafer 4 can be attained bymaking the intensities of diffracted beams observed on both sides equaltogether. It is said that this aligning method can provide a degree ofaligning precision of several hundreds of Å. In this method, however,the alignment between the photo mask 2 and the wafer 4 is largelyaffected by the distance D between the photo mask 2 and the wafer 4, sothat it is necessary to control the distance D with a high degree ofaccuracy. In addition, this method requires an impractically complicatedapparatus because the aligning operation has to be made with the photomask 2 and the wafer 4 being positioned close to each other with precisecontrol of the distance D therebetween.

In order to align elements having a line width of sub-micron order, ithas been proposed to observe the discharge of secondary electron fromthe elements This, method, however, is also impractical because thismethod cannot be carried out in the atmosphere and, hence, thethrough-put is too small in the production of LSI.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a positiondetecting method possibly used in an aligning method which permitsalignment of minute patterns, particularly accurate and easy alignmentof patterns of photo .Iadd.mask .Iaddend.and wafer in the production ofLSIs, within the atmosphere with a simple arrangement.

It is another object of the invention to provide an aligning methodwhich permits alignment of minute patterns of photo mask and wafer inthe production of LSIs by a simple arrangement within the atmosphere, aswell as a method of exposure which is conducted after the alignment.

According to one aspect of the invention, coherent ray beams are appliedfrom two directions such that these two ray beams interfere with eachother to form interference fringes. A grid is disposed in the paths ofthe ray beams in parallel with the interference fringe, and the raybeams reflected by or transmitted through this grid are focused througha lens. By this method in which, by measuring the intensity of the thusfocused ray, the relative position between the interference fringe ofthe two ray beans and the grid is detected, the alignment of minutesemiconductor elements can be made with a high degree of accuracy.Furthermore, by selecting the pitch of the grid on a substrate to be ntimes as large as the pitch of the interference fringes (n being aninteger), the grid for alignment is formed by a photolithographictechnique simultaneously with the formation of the LSI pattern, therebypermitting the alignment with high accuracy.

According to a further aspect of the invention, there is provided analigning method for attaining alignment between two substrates, e.g. areticle and a wafer. A coherent first ray beam is applied to the reticleon which a diffraction grid for a first ray beam is provided. The firstray beam is diffracted by this grid into a second ray beam which in turnis applied to the wafer to which is also applied a third ray beam whichcan interfere with the second ray beam. By measuring the intensity ofthe ray beam reflected by or transmitted through the diffraction grid onthe wafer, it is possible to attain alignment between the.[.interfere.]. .Iadd.interference .Iaddend.fringe of two ray beamsapplied to the wafer and the grid formed on the wafer.

According to a still further aspect of the invention, there is providedan aligning method in which a coherent first ray beam is applied to thefirst one of two substrates to be aligned with each other. The thusapplied first ray beam is diffracted into a second ray beam by a firstdiffraction grid provided on the first substrate. The second ray beamobtained through diffraction by the first diffraction grid is applied tothe second substrate to which also is applied a reference third ray beamwhich can interfere with the second ray beam. The second and the thirdray beams impinge upon a second diffraction grid and a fourth ray beam,which is reflected by or transmitted through the second diffractiongrid, is lead to a photo detecting means adapted to measure theintensity of this ray beam. By this measurement, the relative positionbetween the second diffraction grid on the second substrate and theinterference fringe of the second and third ray beams applied to thesecond substrate is detected to permit the alignment between the firstsubstrate and the second substrate.

An aligning apparatus for carrying out the method of the inventioncomprises, for example, a beam splitter adapted to split a ray beamhaving coherency into two ray beams, two reflecting mirrors arranged toapply the reflected ray beam and transmissed ray beam from the beamsplitter to a grid on a wafer at a substantially equal angle θ, twophoto-detectors adapted to receive the reflected ray diffracted by thegrid on the wafer through respective slits, and a ray intensitymeasuring circuit adapted to measure, from the outputs of twophoto-detectors, the degree of parallelism and the relative position inthe pitch direction between the grid and the interference fringe of tworay beans. According to this arrangement, it is possible to measure thedegree of parallelism, as well as the relative position in the pitchdirection, between the interference fringe of two ray beams and the gridand, hence, to conduct the alignment of a semiconductor element at ahigh accuracy.

In addition, the invention permits also an exposure after theaccomplishment of accurate alignment through detection of the relativeposition between the interference fringe of two ray beams and the grid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a plan view of a conventional aligning mark on a photo mask;

FIG. 1b is a plan view of a wafer illustrating a conventional aligningmethod;

FIG. 2 is an illustration of a conventional aligning method;

FIG. 3 is a schematic illustration of a reflection type aligning systemin accordance with the invention;

FIG. 4 is a schematic illustration of a transmission type aligningsystem in accordance with the invention;

FIG. 5 is a diagram showing the observation angle dependency of the rayintensity observed by a photo-detector;

FIG. 6 is a diagram showing the deviation dependency of the rayintensity observed by a photo-detector;

FIG. 7 is a diagram showing the angle dependency of the ray intensityobserved in the aligning method of the invention employing a grid havinga pitch which is n (n being an integer) times as large as the pitch ofthe interference fringe;

FIG. 8 is a diagram showing the grid position dependency of the rayintensity as observed in the aligning method of the invention;

FIG. 9 is a plan view of a wafer illustrating the alignment of thepattern of the wafer;

FIG. 10 is a plan view illustrating a method in which the aligningmethod of the invention is used in combination with a conventionalaligning mark;

FIGS. 11a and 11b are illustrations of alignment achieved by thealigning marks as shown in FIG. 10;

FIG. 12 is an illustration of an embodiment of the aligning method ofthe invention for achieving an alignment between a wafer and a reticle;

FIG. 13 is an illustration of the relative position between a grid andan interference fringe of two ray beams used in the aligning method ofthe invention;

FIG. 14 is a plan view of an example of a grid on a wafer, used in thealigning method of the invention;

FIG. 15 is an illustration of arrangement of constituents of an aligningsystem for carrying out the aligning method of the invention, as well asthe operation of these constituents;

FIGS. 16a and 16b are illustrations of an aligning method in accordancewith the invention;

FIG. 17 shows an arrangement for carrying out another embodiment of thealigning method of the invention;

FIGS. 18a and 18b are illustrations of the aligning method as explainedin connection with FIG. 17;

FIG. 19 is a schematic illustration of arrangement for carrying outstill another embodiment of the aligning method of the invention;

FIG. 20 is a plan view of a pattern on a reticle;

FIG. 21a is an illustration of a further embodiment of the aligningmethod of the invention;

FIG. 21b is a plan view of a diffraction image;

FIG. 22 is an enlarged plan view of an example of slit used in thealigning method of the invention;

FIGS. 23 and 24 are plan views showing the relationship between theinterference fringes of two ray beams and a grid before the alignment;

FIG. 25 is a graph showing how the ray intensity is affected by therotational angular deviation between the interference fringe and a gridas observed when a slit is disposed with its longer side extendedsubstantially in parallel the interference fringes;

FIG. 26 is a graph showing how the ray intensity is affected by therotational angular deviation between the interference fringes of two raybeams and a grid as observed when a slit is disposed with its longerside extending substantially perpendicularly to the interference fringe;

FIG. 27 is a graph showing how the ray intensity is affected by thedeviation in the pitch direction as observed in the aligning method ofthe invention;

FIG. 28 is a plan view showing another example of the slit as used inthe aligning method of the invention;

FIG. 29a is an illustration of alignment between a photo mask and awafer for a proximity exposure, as well as the exposure process;

FIG. 30 is a plan view of an aligning mark on a photo mask;

FIG. 31 is a plan view of an aligning mark formed in the grid of awafer;

FIGS. 32a and 32b are illustrations of alignment between an aligningmark on a photo mask and a grid aligning mark on a wafer;

FIG. 33 shows the general arrangement of the exposure system forcarrying out an embodiment of the exposure method of the invention;

FIG. 34 is a plan view of a specimen W having a grid G used in theexposure system shown in FIG. 33;

FIG. 35 is a plan view of a mask B used in the exposure system, having aplurality of windows B1 and B2;

FIG. 36 is a partly-sectioned view of a fine adjustment mechanism A ofthe exposure system as viewed in the direction of the optic axis z;

FIG. 37 is a sectional view of the fine adjustment mechanism A and aray-path partial intercepter taken along a z-y plane;

FIG. 38 is a view of the fine adjustment mechanism A of the system asviewed in the direction of the optic axis z;

FIG. 39 is a plan view of a mask 63 incorporated in the exposure system,having windows C₁ and C₂ ;

FIG. 40 is a plan view showing the detail of the groove in a rotaryring;

FIG. 41 is a view of a ray-path whole intercepter D as viewed in thedirection of the optic axis z;

FIG. 42 is a sectional view of the ray-path whole intercepter D takenalong the plane z-y;

FIG. 43 is a plan view of a specimen having a diffraction grid G used inthe exposure system;

FIG. 44 is an illustration of the path of a reflected ray R1 afterdiffraction by the diffraction grid G in the exposure system;

FIG. 45 is an illustration of the path of the reflected ray R2 afterdiffraction by the diffraction grid G2 in the exposure system;

FIG. 46 is a plan view of a ray-receiving element as used in theexposure system;

FIG. 47 is a front elevational view of reflecting mirrors M1 and M2 asused in the exposure system;

FIG. 48 is a side elevational view of the reflecting mirrors M1 and M2;and

FIG. 49 is an illustration of the paths of the diffracted rays R₁₀, R₁₁,R₂₀ and R₂₁ under the condition of Φ₁ ≠(-Φ₂), Φ₁ ≠(-Φ_(d1)) and Φ₂≠(-Φ_(d21)), in the exposure system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 shows a position detecting system for carrying out an aligningmethod of the invention, provided with a holographic exposure device anda photodetector in accordance with the invention. A coherent ray beam 10from a laser source is applied to a beam splitter BS which makes anamplitude split of the beam into a reflected ray beam 11 and atransmitted ray bean 12 of the substantially equal intensity. These raybeams 11 and 12 impinge upon and are reflected by reflecting mirrors M₁and M₂ so as to impinge upon a wafer W which is a substrate of asemiconductor. The constituents BS, M₁, M₂ and W are so arranged thatthe ray beams reflected by the reflecting mirrors M₁ and M₂ impinge uponthe surface of the wafer W at a substantially equal incident angle θ.The wafer W has a grid G formed therein. The reflected ray beam afterdiffraction by the grid G, represented by 13 and 14 respectively, comeinto photo-detectors D₁ and D₂ through lenses L₁ and L₂, respectively.The grid G may be constituted by a repetitional pattern formed regularlyon a predetermined region of the wafer W.

Representing the wavelength of the laser beam by λ and the pitch of theinterference fringes of reflected ray beams 11, 12 from mirrors M₁, M₂by Λ, the interference fringes formed on the wafer can be expressed by

    Λ=λ/2 sin θ

The grid G having a pitch substantially equal to the pitch Λ of theinterference fringe produces a ray beam which is formed by awave-surface splitting of a ray beam that is obtained throughinterference between two ray beams 11 and 12. The ray beams obtainedthrough the wave-surface splitting are focused through the lenses L₁ andL₂ and are made to interfere with each other. By so doing, it ispossible to obtain a ray intensity information concerning the positionalrelationship between the interference fringes of two ray beams and thegrid G.

The intensity I of the ray beam observed by the photo-detectors D₁ andD₂ are given by the following equation (1).

    I=U.sub.A.sup.2 +U.sub.B.sup.2 +U.sub.a *U.sub.B +U.sub.A ·U.sub.B *                                                         (1)

where, U_(A) and U_(B) represent, respectively, amplitude intensities ofthe ray beams 11 and 12, while U_(A) * and U_(B) * represent theconjugate complex amplitudes.

Thus, U_(A) and U_(B) are given by the following equation (2). ##EQU1##where, A and B represent constants, N represents the number of grids, δAand δB represents the optical path difference between rays diffracted bytwo adjacent grids, x represents the relative positional relationshipbetween the grid and the interference fringes of ray beams 11 and 12 andθ_(A) and θ_(B) represent the angles formed between a line normal to thewafer and the ray beams 11 and 12, respectively.

FIG. 5 shows the observation angle dependency of the ray intensity I.Four peaks appear while the observation angle is continuously changedbetween -π/2 and π/2 past 0. The diffracted rays of the 0 order of theincident ray beam 11 and 12 are overlapped together in the peaksappearing at the angles -θ₁ and θ₁, while the peaks appearing at angles-θ₂, θ₂ contain diffracted ray beams of the first order of the incidentray beams 11 and 12. These diffracted ray beams contain the positionalinformation concerning the relative position between the interferencefringe formed by the ray beams 11, 12 and the grid on the wafer. FIG. 6shows how the ray intensity I is changed when the relative position xbetween the interference fringe of the ray beams 11, 12 and the grid isvaried while the photodetector is fixed at a position where a peak isobserved in FIG. 5. It will be seen that the ray intensity is changedperiodically as the relative position x is changed by a distance equalto the pitch 1 of the grid. It is, therefore, possible to obtain therelative position between the interference fringe and the grid byobserving the ray intensity.

From this description it will be understood that the relative positioncan be detected practically by a single photodetector, although thearrangement shown in FIG. 3 employs two photo-detectors. The use of twophotodetectors at mutually conjugate positions as shown in FIG. 3,however, offers the following advantages. Namely, since the intensity ofthe diffracted ray varies due to the difference of diffractionefficiency of the tapered portions of concavity and convexity of thegrid, it is possible to read the positional information more accuratelyby observing the difference between the outputs from two photodetectors.Furthermore, through the observation of the difference of the output, itis possible to delete the noise coming into respective photodetectors sothat the detection of position can be made at a higher accuracy.

If the grid G is a blaze grid, the ray beams coming into twophotodetectors have an .[.asymmetry.]. .Iadd.asymmetrical.Iaddend.relationship to each other, even if the grid G and the raybeams 11, 12 are set in symmetry. Consequently, only one of thephotodetectors can produce a large output while the other can produce anoutput the level of which is too low for the level of the noise. Thus,the accuracy of the observation differs extremely depending on themanner of setting of the blaze grid if the observation is made onlythrough one of the photodetectors. In such a case, the influence of themanner of setting of the blaze grid can be eliminated and therelationship between the ray intensity and the position can bedetermined to higher accuracy by observing the sum of the outputs fromtwo detectors.

FIG. 4 shows the case where the ray beams led to the photodetector aretransmitted ray beams. In this case, the optical path from the ray beamsource to the grid is indentical to that in FIG. 3. The ray beams whichhave been transmitted through the grid G form high intensities ofdiffracted ray beam at angular positions θ₁ and θ₂. More specifically,at the angular position θ₁, the ray beam 12 is received directly and theray beam interfered with the ray beam diffracted from the ray beam 11 isintroduced to the photodetector 3 through the lens L₁. By settinganother photodetector at the conjugate position, a ray intensityconjugate to the photodetector D3 is observed. Then, by observing thedifference .[.and.]. .Iadd.or .Iaddend.the sum of the outputs ofconjugate photodetectors, it is possible to enjoy the same advantage asthat described before in connection with the first embodiment.

By setting the photodetector at the angular position θ₂, it is possibleto observe the ray beam which is produced on the photodetector D₄ as aresult of interference between the diffracted ray beam of -1 order ofthe ray beam 11 and the diffracted ray beam of -2 order of the ray beam12 applied through the lens L₂. In this case, all of the observed raysare diffracted ray beams so that the noise, i.e. the ray beams from theportion devoid of the grid, is not allowed to come into thephotodetector, unlike the case where the photodetector is located at theposition D₃. By measuring the interference of ray beam at the positionD₄, therefore, it is possible to detect the position more accuratelythan the case where the observation is made at the position D₃.

By placing the photodetector at the focal point of the condenser lensfor effecting the interference, every part of the ray beam impingingupon the lens is put into interference so that a high sensivitiy of rayintensity is obtained. On the other hand, if the arrangement is suchthat the interference ray beam is measured by way of a slit whileoffsetting the photodetector from the focal point of the lens, it ispossible to measure the interference of a part of the ray impinging uponthe lens. In such a case, the accuracy is improved although thesensitivity is lowered.

In a third embodiment, the relative position x between the grid G andthe interference fringe of two ray beams is varied and the relativeposition is compared with the maximum or minimum value of the rayintensity.

In the first and second embodiments described before, the relativeposition x between the grid G and the interference fringe of two raybeams is obtained through measuring the ray intensity. This rayintensity, however, is a cosine function so that there is a practicallimit in obtaining the higher accuracy of the positional informationthrough enhancement of accuracy of reading of the ray intensity withoutchanging the pitch l of the grid. A more accurate detection of positionis possible by memorizing the grid positions where the maximum and/orminimum ray intensity is obtained, calculating the feed pitch anddividing the calculated feed pitch. The observation of the feed pitch ispreferably made by a scale proportional to the feed pitch, e.g. angle,length and the like.

In a fourth embodiment, at least two photodetecting means are providedfor independent observation of ray intensities. In view of that, thedirect incidence of the ray of 0 order to the photodetector D₃ in thesecond embodiment, a portion devoid of the grid is provided in theregion of the grid in the fourth embodiment, the photodetectors areoffset from the focal point to make the ray beams interfere throughslits to obtain intensity of interference of part of the rays. With thisarrangement, it is possible to effect the alignment by comparing theoutputs from two photodetectors. On the other hand, a photodetectorconstituting the aforementioned other system is used as thephotodetector D₄. With this arrangement, it is possible to obtain theparallelism and alignment between the interference fringe and the gridG. Thus, the aligning operation can be accomplished in a shorter periodof time by conducting the alignment by two systems.

According to the invention, it is possible to effect the alignment ofphoto mask in the same manner as that described hereinbefore, by forminga grid in the photo mask.

As above-mentioned, FIG. 4 shows the arrangement of an aligning systemwhich is used when the wafer is of the type which permits transmissionof a ray there-through. In this system, the photodetectors D₃ and D₄ andthe optic systems L₁ and L₂ are disposed behind the wafer W.

FIG. 7 shows an observation angle-dependency of the ray intensity I, asobtained when the pitch of the interference fringe is 1 μm, while thepitch of the grid is 2 μm. As will be seen from the curve showing theray intensity I, sharp peaks of the ray intensity appears only when thepitch of the grid is n (n being an integer) times as large as the pitchof the interference fringe. It will be seen that five peaks appear asthe observation angle is continuously changed between 0 and π/2.Diffracted ray beam of 0 order of the incident rays 11 and 12 aresuperposed in the peak appearing at θ₂, while the peak θ₄ contains thediffraction ray beam of the first order of the peak of θ₄. The peaksappearing in the angular range of between θ₁ and θ₅ contain theinformation concerning the relative position between the interferencefringe and the grid on the wafer.

FIG. 8 shows how the ray intensity I is changed as the relative positionx between the grid on the wafer and the interference fringe formed bythe ray beams 11 and 12 is changed while the photodetector is fixed atthe position where the peak is obtained in FIG. 4. The ray intensity isperiodically changed corresponding to the change of the relativeposition x by the distance equal to the pitch l of the grid.

In the actual formation of the LSI pattern, the aligning operation ismade to attain an alignment between the pattern of the circuit elementportion formed on the wafer and the interference fringe of two ray beamsto be exposed. FIG. 9 shows how this aligning operation is actuallyconducted. A diffraction grid 20 and the gate pattern 21 are formed onthe wafer W by a conventional photolithographic technique. Thediffraction grid 20 is precisely positioned with respect to the gatepattern 21 and can be provided, for example, in the margin or scribeline for severance of adjacent chips from each other. The grid 20 has aline width which is n (n being an integer) times as large as theinterference fringe pitch falling within such a range as permitting anaccurate formation by a light ray exposure or an X-ray exposure. Theinterference fringe 22 is applied to the whole part of the wafer or tothe aligning grid 20, thereby to permit the alignment between the grid20 and the interference fringe 22, as well as the alignment between thepattern 21 and the interference fringe 22.

FIG. 10 shows an aligning pattern consisting of a combination of aconventional aligning mark MK and the grid G. As will be understood fromthis Figure, a crusiform-shaped aligning mark MK is formed in thepattern of the grid G. As two ray beams are applied to this patternhaving the crusiform-shaped aligning mark, the diffracted ray beam formsthe pattern shown in FIG. 10 .[.form.]. .Iadd.from .Iaddend.an imagewhich is constituted by a rectangular, bright pattern having acrusiform-shaped dark pattern. If the alignment is insufficient, thecrusiform-shaped dark pattern is doubled as shown in FIG. 11a. Theadjustment, therefore, is made to make the two crusiform-shaped patternssuperposed with each other as shown in FIG. 11b. By providing thephotodetecting means corresponding to the crusiform-shaped pattern, itis possible to conduct the alignment of the pattern in the same way asthat in the conventional aligning method. It is thus possible to effectan approximate alignment on the order of 0.3 micron by the same aligningmethod as that of the conventional aligning method. After the completionof the alignment in the manner described hereinbefore, a Moire fringecomes to appear in the bright rectangular pattern, and the alignment canbe achieved at a high degree of accuracy in a short period of time bymaking use of this fringe.

As has been described, with the described embodiments of the aligningmethod of the invention, it is possible to attain a highly accuratealignment between the pattern on the wafer and the pattern to be exposedin the exposure system for the production of semiconductor devices. Theexposure which is conducted following the aligning operation can be madeby the exposure of .Iadd.an .Iaddend.interference fringe of two raybeams by for example .Iadd.a .Iaddend.holographic method, conventionalphotolighography, scale-down projection exposure, X-ray exposure,electron-beam exposure and so forth.

FIG. 12 shows the principle of a scale-down projection exposure systemcarrying out an embodiment of the aligning method of the invention, aswell as an arrangement for attaining an alignment between a reticle anda wafer.

An explanation will be made first as to the arrangement for ordinaryscale-down projection exposure. The exposure system includes a raysource, reticle R, lens system L and a semiconductor wafer W which aredisposed in the mentioned order. The parallel ray beam 111 coming fromthe ray source is partially intercepted by the pattern on the reticle Rand the ray beam from the reticle R having a predeterminedlight-and-shade pattern is condensed by the lens system L to form aprojection image R' of the reticle on the wafer.

The arrangement used for the alignment is as follows. Namely, a coherentray such as a laser beam is applied to a beam splitter which effects anamplitude aplitting into two ray beams 112, 113 of a substantially equalray intensity. The two ray beams 112, 113 are applied to diffractiongrids 114, 115 which are provided on the reticle R. The arrangement ofthe reticle R can be represented by the phases and angles Φ₁, Φ, of theincident ray beam and the diffracted ray beam. The constituents such asR, L and W are so arranged that the diffracted rays 116, 117 from thereticle R pass through the lens system L and interfere with each otheron the wafer W. As will be seen from FIG. 13, a diffraction grid G isformed on a portion of the wafer W, and the interference fringe F ofthese two ray beams is formed on this grid G. The reflected ray 118after the diffraction by the grid G is led to the photodetector D. Asshown in FIG. 14 by way of example, the grid G on the wafer ispreferably constituted by a regular repetitional pattern provided on apredetermined region of the wafer.

As will be seen from FIG. 13, the interference fringe F formed byinterference between two ray beams has a pitch. A corresponding to theincidence angle θ of a regular pitch. The grid G, which has a pitchsubstantially equal to the pitch Λ of the interference fringe, providesa ray beam which is obtained by diffracting the ray formed byinterference between two ray beams 116 and 117. With this diffracted raybeam, it is possible to obtain a ray intensity information representingthe positional relationship between the interference fringe F of two raybeams and the grid G. The intensity of the ray observed on thephotodetector D is given by the equation (1) and the principle of thealignment is same as that of the embodiments described before.

An explanation will be made hereinunder as to the procedure forattaining alignment between the reticle R and the wafer W, with specificreference to FIG. 15.

Two ray beams coming into the reticle R impinge upon the reticle R at aright angle thereto. The arrangement is such that two ray beams 112, 113impinge upon the grids 114 and 115 on the reticle. The grids 114 and 115transmits two ray beams and emits diffracted rays 116 and 117. Since theoptic system is arranged such that the phases of two ray beams 112, 113impinging upon the grids 114, 115 are equal to each other, the wavesurfaces of the rays 116, 117 diffracted by the grid are in symmetrywith each other. As the two ray beams 116, 117 of the same phaseintersect on the surface of the wafer W at an intersecting angle of 2θ,an interference fringe of regular change of light-and shade, denoted byF in FIG. 15, is formed and the position of the interference fringe F isfixed at the position where the wave surfaces intersect each other. Thediffraction grid G (see FIG. 15) formed on the wafer W is aliged withthe interference fringe F at the fixed position.

The relative rotation .[.(adimuth).]. .Iadd.(azimuth) .Iaddend.Φ betweenthe grid G on the wafer W and the interference fringe F of two ray beamswithin the plane of the wafer W can be detected through the observationof the rotation of the Moire fringe formed between the grid on the waferand the interference fringe. The adjustment is then made by finelymoving the wafer in such a manner as to decrease the number of the Moirefringe.

The rotation (tilt) Φ of the grid on the wafer and the interferencefringe of two ray beams within the plane of incidence of the ray beamscauses the same state as that produced when the pitch of theinterference fringe has become large as compared with the pitch of thegrid on the wafer, so that a tile adjustment can be made by decreasingthe number of the Moire fringes as in the case of the adimuth adjustmentexplained above. It the optic paths are arranged in symmetry, the ray of0 order reflected by the diffraction grid G returns to the ray source sothat the tilt adjustment of the wafer can be conducted also by detectingthe change of position of the reflected ray attributable to the shiftingof the wafer.

After making the .[.adimuth.]. .Iadd.azimuth .Iaddend.and tiltadjustments as described, the alignment of the patterns in the reticleand the wafer is conducted in accordance with the principle asrepresented by the equation (1) and (2) mentioned before.

FIG. 14 shows a second embodiment of the invention in which the grid Gformed on the wafer W has a pattern composed of a stripe-shaped gridpattern and a conventional crusiform-shaped mark M formed by removingparts of the stripe-shaped pattern. With this arrangement, it is periodof time.

The diffracted ray from the grid pattern on the wafer W shown in FIG. 14forms an image which is composed of a bright rectangular pattern and adark crusiform-shaped pattern in the bright pattern, as will be seenfrom FIG. 16a. The diffracted ray beam of one incident ray beam 112forms an image of a pattern d₁, while the diffracted ray beam of theother incident ray beam 113 corresponds to the image of the pattern d₂.When viewed from the same side as the photodetecting means, thecrusiform-shaped dark pattern is doubled if the alignment has been madeimperfectly. By providing a photodetecting means corresponding to thecross-shaped pattern and effecting the adjustment of relative positionbetween the wafer and the reticle such that the crusiform-shapedpatterns images is superposed together, it is possible to effect thealignment of the patterns by the same method as the conventional method.Namely, the embodiment permits an approximate alignment on the order of0.3 micron which has been accomplished by the conventional aligningmethod. When this alignment has been accomplished, Moire fringe comes toappear in the rectangular bright pattern as shown in FIG. 16b. It ispossible to attain a highly accurate alignment in a short period oftime, by the aligning method of the invention making use of the Moirefringe.

FIG. 17 shows a third embodiment which differs from the secondembodiment in that the grid patterns 119, 120 on the reticle R includefigure patterns of periods different from those of the grid patterns,e.g. linear patterns. Due to the use of the figure patterns, offset ofthe diffracted rays 118 takes place as shown in FIG. 18a if thealignment has been made imperfectly. In this case, therefore, anapproximate alignment on the order of 0.3 μm can be achieved as in thecase of the conventional aligning method, by a method similar to themethod which has been explained already in connection with FIGS. 16a and16b. In this case, however, since figure patterns are formed in thegrids 119, 120 on the reticle R, it is possible to move the reticle Rinto alignment with the wafer W while fixing the wafer W. Aftercompletion of this approximate alignment, a fine alignment is conductedin accordance with the aligning method of the invention in the mannerexplained before in connection with FIG. 16b, using the Moire fringes asshown in FIG. 18b.

FIG. 19 shows still another embodiment of the aligning method inaccordance with the invention. This embodiment differs from theembodiments shown in FIGS 12 and 15 in the following point. Namely, inthe embodiments shown in FIGS. 12 and 15, two diffraction grids areprovided on the reticle and coherent rays are applied to these grids topermit the information concerning the position of the reticle to beexposed in terms of diffraction angle. In contrast, in the embodimentshown in FIG. 19, the reticle R has only one diffraction grid 121 towhich a coherent ray 121 is applied to permit the information concerningthe reticle position by means of diffraction angle, and the diffractedray 125 is applied to the wafer W. A reference ray beam 123 which caninterfere with the ray beam 122 is reflected by a mirror 124 and isapplied to the wafer W on which it is made to interfere with thediffracted ray 125 to form interference fringe which carries theinformation concerning position. The ray 126 reflected by the wafer W isapplied to the photodetector. Therefore, at the position of thephotodetector D which receives the reflected ray 126 from the wafer W,it is possible to effect the coarse and independent alignment of thewafer W by applying only the reference ray 123 to the grid. Then, byapplying the ray 125 diffracted by the grid on the reticle R to thewafer, it is possible to attain an alignment with a high degree ofaccuracy equivalent to that performed by the method explained inconnection with FIGS. 12 and 15.

FIG. 20 shows a further embodiment of the invention which differs fromthe embodiment shown in FIG. 13 in that the pitch of the grid on thewafer is selected to be n (n being an integer) times as large as thepitch of the interference fringe, so that the alignment can be achievedwith a high degree of accuracy even with the use of an aligning markwhich is obtained by the conventional exposure method.

A diffraction grid 130 formed in, for example, the scribe line of thereticle R and the gate pattern 131 of a MOS transistor as a circuitelement are disposed on the reticle R with a high degree of accuracy.The diffraction grid 130 includes a crusiform-shaped aligning mark (notshown in FIG. 20) as shown, for example, in FIG. 21a. A referencenumeral 132 appearing in FIG. 20 designates a interference fringe formedon the wafer. As in the case of the arrangement shown in FIG. 17, laserbeams 112 and 113 impinge upon the grid 130 to permit the alignment suchthat the aligning pattern on the reticle is aligned. The pattern (aprojected image of the grid 130) is designated at numeral 133 in FIG.21a. To this pattern 133, the grid 134 on the wafer W is superposed asthe aligning pattern for alignment with the crusiform mark. Since thisgrid 134 is formed on the wafer W by the conventional ray exposure, itis not possible to obtain the thin pattern of the line width comparingwith the line width of the interference fringe as obtained through theinterference fringe exposure attained by the laser holography inaccordance with the invention. Therefore, if the pitch of the grid 134on the wafer W is selected to be n(n being an integer) times as large asthe pitch of the interference fringe 132, a diffraction image of thepattern consisting of the crusiform-shape and the aligning pattern 134on the wafer superposed to each other is obtained as the position of thephotodetector D, as shown in FIG. 21b. It is possible to effect a highlyaccurate alignment by making use of the Moire fringe of this diffractionimage.

The wavelength of the laser beam for alignment is preferably selected soas not to affect the resist formed on the wafer. The alignment and theexposure will be facilitated if the alignment is conducted with, forexample, red ray, while effecting the exposure by ultraviolet rays as inthe case of the conventional exposure.

In the aligning method of the invention, a higher sensitivity foralignment can be achieved by adding a slit to the portion of the opticpath ahead of the photodetector.

FIGS. 23 and 24 show positional relationship between the interferencefringe of two ray beams and the grid 218 before the alignment. In theseFigures, K represents the interference fringe, α.sub.θ represents theangle formed between the interference fringe K and the grid 218 and xrepresents the deviation of pitch between the interference fringe K andthe grid 218.

A change of ray intensity I as shown in FIG. 25 is obtained as the wafer217 is rotated by a slight angle around a line normal to the planecontaining the grid 218, while leading the ray beams to thephotodetectors D₁ and D₂ through slits 221 and 222. More specifically,in FIG. 25, the axis of ordinate represents the ray intensity I, whilethe axis of abscissa represents the amount a of rotation. The level ofthe peak value of the ray intensity varies depending on the shapes ofthe slits 221 and 222. More specifically, FIG. 25 shows the change inthe ray intensity I as observed when the slits 221 and 222 are arrangedsuch that their longitudinal sides L_(a) are extended substantially inparallel with the interference fringe, while FIG. 26 shows the change ofthe ray intensity I as observed when the slits are disposed such thattheir longitudinal sides L_(a) extend substantially perpendicularly tothe interference fringe. A symbol L_(b) shows the breadthwise directionof the slit. As will be seen from FIGS. 25 and 26, it will be seen thatthe a higher sensitivity of the ray intensity information to therotation is obtained by arranging the slits 221, 222 with their longersides L_(a) substantially parallel to two ray beams. Namely, in thisembodiment of the invention, the change in the ray intensity becomesgreater as the angle α.sub.θ formed between the grid 218 and theinterference fringe of two ray beams approaches zero. This change in theray intensity appears in the direction parallel to the interferencefringe K. That is, the ray intensity change becomes more distinguishableas the length of the longer sides L_(a) becomes greater under thecondition of the length of the longer sides L_(a) greater than thelength of the breadthwise side L_(b).

When the ray intensity takes its peak value, the angle α.sub.θ formedbetween the interference fringe K and the grid 218 becomes zero. Inother words, the interference fringe K and the grid 218 become parallelto each other.

FIG. 28 shows a modification in which three slits are used: namely, aslit 225 parallel to the interference fringe of two ray beams, a slit226 inclined at a predetermined angle BA with respect to the slit 225,and a slit 227 which is inclined at a predetermined angle BB to the slit225. In this case, photodetectors 228, 229 and 230 are disposed atpositions corresponding to respective slits. By comparing the outputsfrom these three photodetectors, it is possible to detect the directionof rotation for reducing the angle α.sub.θ between the interferencefringe K and the grid 218 to 0 (zero).

Although in the described embodiment the alignment is achieved byrotating the wafer 27, it is possible to obtain the same effect byrotating two ray beams instead of rotating the wafer 217.

FIG. 27 shows the change of the ray intensity I as observed when thewafer 217 is slightly moved in the direction of the pitch of theinterference fringe formed by the interference between two ray beams. Inthis embodiment, the axis of ordinate represents the ray intensity I,while the axis of ordinate shows the amount x of movement. It will beunderstood that the ray intensity I is periodically changed at the samepitch as the pitch P of the grid. The small fluctuations of the rayintensity I are attributable to the feed at a fine pitch. When the rayintensity I takes the peak value, the shift x in pitch between theinterference fringe K and the grid 218 becomes zero.

In this embodiment, the alignment is achieved by moving the wafer 217.An equivalent effect, however, can be obtained by moving two ray beamsinstead of the wafer 217. It does not matter that either the alignmentin the rotational direction or the alignment in the direction x of pitchis made first. The alignment in two directions is accomplished when theray intensity I takes the peak value, and the aligning accuracy isenhanced as the ray intensity I approaches the peak value.

FIG. 29 shows a different embodiment in which a grid 232 is positionedat the point of intersection of the scribe lines 231 of the wafer, at45° inclination to the scribe line 231. According to this arrangement,it is possible to avoid the formation of diffraction image of eachpattern provided on the wafer 217 and, hence, to achieve the alignmentwith a high degree of accuracy.

A description will be made hereinunder as to an embodiment in which thealignment is achieved between the interference fringe of two ray beamsand a grid for a subsequent proximity exposure as is the case of theX-ray exposure. A photo mask M and a wafer W are arranged in closeproximity with each other as shown in FIG. 29a. An alignment is effectedbetween the interference fringe of two ray beams and the aligning gridG₁ on the photo mask as has been described already. The photo mask isfurther provided with a transparent aligning window H so that thealignment of the wafer W for the proximity exposure is conducted throughthis window. An aligning grid G2 for alignment is provided on the waferW, and the positions of the grids G₁ and G₂ can be determined accuratelyat every one pitch of the interference fringe.

Assume here that a conventionally used aligning mark such as acrusiform-shaped mark as shown in FIG. 30 is formed in the window H ofthe photo mask M, while a crusiform-shaped mark is formed in the grid G₂on the wafer as shown in FIG. 31. Then, an alignment is made toapproximately align the crusiform-shaped mark shown in FIG. 30 and thecrusiform-shaped mark shown in FIG. 31. In FIG. 32a, a reference symbold₁ denotes a pattern formed on the wafer W, while d₂ represents apattern on the mask. An aligning operation is conducted to make m₁ andm₂ align with each other. Then, a fine alignment is accomplished byaligning operation making use of the interference fringe of two raybeams as shown in FIG. 32b. Thus, the alignment of the photo mask isconducted once when the photo mask is set and the transfer is maderepeatedly on wafers using this photo mask. After the completion ofalignment, exposure is conducted by proximity exposure method making useof X-ray, ion beams and ultra-violet rays.

Major optic systems for carrying out the aligning method and exposuremethod of the invention have been described. An explanation will be madehereinunder as to a holographic exposure system as a practical exampleof such optic systems.

FIG. 33 shows the general arrangement of the exposure system embodyingthe present invention. In operation, a coherent ray RA is emitted from alaser source 310, and is introduced to a lens 313 through reflectingmirrors 311, 312, and is diversified by a pin hole 314 and changed intoparallel ray beam through a collimating lens 315. The parallel ray beamis then applied to a beam splitter BS and is amplitude-splitted intoreflected ray R₁ and transmitted ray R₂ of a substantially equalintensity.

The amplitude-splitted reflected ray R₁ and the transmitted ray R₂impinge upon the reflecting mirrors M₁ and M₂, respectively, and areapplied to the surface of a specimen W. These constituents BS, M₁, M₂and W are so arranged that the rays reflected by the mirrors M₁ and M₂impinge upon the surface of the specimen at an equal incidence angle θ.

As shown in FIG. 34, grids G are formed in a plurality of .[.block.]..Iadd.blocks .Iaddend.on the specimen W. The reflected rays R₃ and R₄diffracted by the grid G impinge upon the photodetectors D₁ and D₂through the optic systems including lenses L₁ and L₂.

Representing the wavelength of the laser beam by λ and the pitch of theinterference fringe formed by interference of the reflected rays R₁ andR₂ from the mirrors M₁ and M₂ by Λ the pitch of the interference fringeformed on the specimen W is expressed by the following formula. ##EQU2##

The grid G having a pitch substantially equal to the pitch λ of theinterference fringe produces rays which are obtained through adiffraction of the ray formed by the interference between two ray beamsR₁ and R₂, the diffraction being made by the grid which effects awave-surface splitting of the ray beam formed by the interference. Therays produced by the wave-surface splitting are converged through theoptic systems of the lenses L₁ and L₂ and are made to interfere witheach other. By so doing, it is possible to obtain by photodetectors D₁and D₂ a ray intensity which represents the positional relationshipbetween the interference fringe formed by two ray beams and the grid G.

By making use of this ray intensity representing the positionalrelationship, it is possible to detect the positional relationshipbetween the specimen W and the interference fringe of two ray beams andto correct the position of the specimen W, thereby to attain alignmentbetween the interference fringe of two ray beams and the specimen W.

A z axis is assumed here as being the central axis z--z of optic pathsof the reflected ray beam R₁ and the transmitted ray R₂. The specimen Wis held by a fine adjusting mechanism A which can hold the specimen Wsuch that its surface carrying the grid G is substantially perpendicularto the z axis and has functions to effect fine adjustment of position inthe x and z axes, as well as in the rotational directions around theaxes x, y and z, the rotational angles being represented by α, β and θ.The positional relationship between the interference fringe and the gridG on the specimen W is adjusted by means of the fine adjusting mechanismA.

A symbol B represents a mask having a form as shown in FIG. 35. The maskB is provided with a plurality of windows B₁ at the portion thereofcorresponding to the position of the grid G so as to pass two ray beams,and at its portion with a plurality of windows B₂ at its portioncorresponding to the exposure position of the specimen W.

A symbol C denotes an optic path partial intercepter having anintercepting mechanism which is adapted to partially intercept two raybeams such that two ray beams are applied only to the grid portion Gwhen the positional relationship between the aforementioned interferencefringe and the specimen W is adjusted, and to intercept two ray beamspartially such that the ray beams impinge only upon the specimen W whenthe exposure is conducted after the alignment.

A symbol DA represents an optic path full intercepter disposed betweenthe laser generator 310 and the reflecting mirror 311 and having anintercepting mechanism adapted to fully intercept the optic path.

The constituents 310, 311, 312, 313, 314, 315, 316, BS, M₁, M₂ and A aremounted on the same vibration damping base so that they are protectedfrom external vibration. The optic path intercepters C and DA aremounted on a base (not shown) different from the vibration damping baseE so that the vibration produced as a result of operation thereof is nottransmitted to the vibration damping base E.

The detail of the fine adjustment mechanism A will be describedhereinunder with specific reference to FIGS. 36 and 37.

A reference numeral 320 designates a specimen holder having a vacuumsucking hole a for sucking and holding the specimen W having the grid Gand a vacuum hole b. The vacuum hole b is connected to a vacuum sourcewhich is not shown. The specimen base 320 is provided also with a vacuumsucking groove c for sucking and fixing the mask B and a vacuum port ddwhich is connected to a vacuum source (not shown). The height of thestep between the surface portion of the specimen holder for sucking thespecimen W and the surface portion of the same for sucking the mask B isselected to be slightly greater than the thickness t of the specimen W.

An explanation will be made hereinunder as to the adjusting mechanism A₀for adjusting the angle α. The specimen holder 320 is fixed through abelleville spring 322 to a θ rotation mechanism A₁ by means of threebolts 321. In order to permit the specimen W to rotate around the x axisby a small angle α, bolts 321 are adapted to be fixed at both ends f andg or the x axis and on one end h on the y axis.

An explanation will be made hereinunder as to the θ rotation mechanismA₁. A reference numeral 323 designates a rocker plate connected to thespecimen base 320 through the belleville spring 322 by means of bolts321. The rocker plate 323 is rotatably held by a rotary guide ring 324so as to be able to rotate smoothly around the z axis. A referencenumeral 325 denotes a θ rotation mechanism base for fixing the rotaryguide ring 324, while a reference numeral 326 denotes an arm which isfixed at its one end to the rocker plate 323. The other end of the arm326 is pressed by a pressurizing unit 328 having a compressing coiledspring 327 so as to rock the rocker plate 323 in the direction ofrotation. A reference numeral 329 designates a differential micrometerhead contacting the arm 326 in the direction for compressing thecompression coiled spring 327. The point of action 329a of thedifferential micrometer head 329 and the point of action 328a of thepressuring unit 328 are disposed at opposite sides of the arm 326. Areference numeral 330 designates a fixing base for fixing thedifferential micrometer head 329 and the pressurizing unit 328. Thefixing base 330 is secured to the θ rotation mechanism base 325. A θrotation drive motor 331 having a reduction gear is fixed to a motormounting base 332 which in turn is fixed to the θ rotation mechanismbase 325. The θ rotation drive motor 331 is connected through a coupling333 to a rotary drum 334 so as to drive the latter. A reference numeral335 designates a slide ring which is pressfitted into a simble 329bannexed to the differential micromotor head 329. The slide ring 335 isfitted in the rotary drum 334. A guide pin 336 is received by theelongated hole 334a in the rotary drum 334 and is fixed to the slidering 335. As the θ rotation drive motor 331 cperates, the rotary drum334 is rotated through the coupling 333 so that the guide pin 336, slidering 335 and the simble 329b make spiral motion and move straight in thedirection of operation of the differential micrometer head 329. As aresult, the arm 326 is pushed so that the rocker plate 323 for fixingthe arm 326 is guided by the rotary guide ring 324 to rotate slightlyaround the z axis. The slight rotation of the rocker plate 323 causes aslight rotation of the specimen holder 320 fixed to the rocker plate323, specimen W held by the specimen holder 320 had the mask B whichalso is fixed to the specimen holder 320.

As the θ rotation drive motor 331 is reversed, the differentialmicrometer head 329 moves straight in the reverse direction.Consequently, the arm 326 is pressed by the spring force of thepressurizing unit 328 so that the rocker plate 323 is rotated around thez axis while being guided by the rotary guide ring 324. Consequently,the specimen holder 320, specimen W and the mask B are rotated slightlyin the counter direction.

Consequently, by the change of the θ rotation drive motor 331, therocker plate 323 rocks by the power of the θ rotation drive motor 331and the spring force of the pressurizing unit 328.

The operation of the θ rotation drive motor 330 by angle θ₁ causes arotation of the rocker plate 323 by an angle Δθ which is given asfollows. ##EQU3## where, S represents the travel or feed per onerotation of the differential micrometer 329, while ll shows the distancebetween the axis of rocking of the rocker plate 323 and the point 329aof action of the micrometer head 329. When the travel is 50 m and ll is100 mm, the angle Δθ of rotation of the rocker plate 323 is calculatedto be 3" (seconds) when the angle θ₁ of operation of the motor is 1°.

The θ rotation drive motor 331 operates under the control of the controlsection (not shown) for an α rotation drive motor. The θ rotary drivemechanism base 325 is fixed to a β rotation mechanism A₂ which has asubstantially identical construction to the θ rotation mechanism A₁,although it is driven not by motor but manually. A reference numeral 337designates a β rocker plate to which fixed is the θ rotation mechanismbase 325. The β rocker plate 337 is rotatably held by the β rotationguide ring 338 so as to be rotated smoothly around the y axis. Areference numeral 339 designates an arm which is fixed at its one end tothe β rocker plate 337, while the other end of the same is pressed by apressurizing unit 341 having a compression coiled spring 340 whichbiases the β rocker plate 337 in the rocking direction. A differentialmicrometer head 342 contacts the arm 339 in the direction forcompressing the compression coiled spring 340. The pressurizing unit 341and the differential micrometer head 342 are fixed to a base 343 whichin turn is fixed to the β rotation guide ring 338. The β rotation guidering 338 is fixed to the z-direction drive mechanism A₃.

To explain in more detail about the z-direction drive mechanism A₃, areference numeral 344 designates a z-axis moving member to which the βrotation guide ring 338 is fixed. The z-axis moving member 344 isslidably held by a z-axis base 346 through two pairs of cross rollerguides 345 so as to be able to slide in the direction of z axis. Adifferential micrometer head 347 is disposed to allow the moving member344 to move in the direction of z axis. The differential micrometer head347 is fixed to a base 348 which in turn in fixed to the z-axis base346. Tension springs 349-1 and 349-2 are fixed to the moving body 344and the z-axis base 346 so as to press the moving body 344 against thedifferential micrometer head 347. The z-axis moving base 346 is fixed toan x-axis drive mechanism A₄.

The x-axis drive mechanism A₄ has the following construction. Areference numeral 350 designates an x-direction moving member which isslidably carried by an x-axis base 352 through two pairs of cross rollerguides 351 for sliding movement in the direction of the x axis. Anx-axis drive motor 353 is fixed to a reduction gear 354 secured to abracket 355 fixed to the x-axis base 352.

A reference numeral 356 designates a coupling through which thereduction gear 354 is connected to the ball screw 357 so that the torqueof the x-axis drive motor 353 is transmitted to the ball screw 357through the coupling 356. Numerals 358 and 359 denote brackets whichaccomodate ball bearings 360, 361, respectively. The brackets are fixedto the x-axis base 352. The ball screw 357 is supported by ball bearings360, 361. A reference numeral 362 designates a nut engaging with theball screw 357 and fixed to the x-axis moving member 350. The torque ofthe x-axis drive motor 353 is transmitted through the reduction gear 354and the coupling 356 to the ball screw 357 so that the x-axis movingmember 350 is moved in the direction of the x-axis through the nut 362.Operation of the x-axis drive motor 353 by an angle θ₂ causes a movementΔx of the x-axis moving member expressed by the following equation.##EQU4##

LL: lead of ball screw 357

Q reduction ratio of reduction gear 354

The amount of movement Δx is calculated to be 0.0025 μm on the conditionof LL=2 mm, Q=1/100 and θ₂ =0.045°.

The x-axis drive motor 353 is under the control of the x-axis drivemotor control section (not shown). The x-axis base 352 is mounted on thevibration damping base E.

An explanation will be made hereinunder as to the optic path partialintercepter C with reference to FIGS. 37 and 38. A reference numeral 363denotes a mask having windows C₁, C₂ formed, as shown in FIG. 39, in theportions corresponding to the windows B₁, B₂ in the mask B mentionedbefore. The windows C₁ and C₂ have lengths and breadths which are Δδgreater than those of the windows B₁ and B₂. A reference numeral 364designates a rotary plate for bonding and fixing the mask 363, while 365designates an intercepting plate for intercepting two ray beams from thewindow C₂ in the mask 363. The intercepting plate 365 is bonded andfixed to an arm 366. A reference numeral 367 designates a fulcrum pinfixed to the rotary plate 364. The arm 366 is so mounted as to be ableto rotate around the fulcrum pin 367. An arm regulating plate 368 isadapted to regulate the movement of the arm 366 such that the latterrotates along the rotary plate 364. A reference numeral 369 denotes aleaf spring which presses the arm 366 against the rotary plate 364.Another leaf spring 370 is arranged to press the arm 366 to the rotaryplate when the arm 366 has been rotated to the position shown byone-dot-and-dash line. A reference numeral 371 designates a yarnretained at its one end by the arm 366 while the other end is fixed to abobbin 372. As the yarn is wound up by the bobbin 372, the arm 366,which has been pressed by the leaf spring 369, is rotated around thefulcrum pin 368 to the position shown by one-dot-and-dash line whilewinding up the yarn. Then, the arm 366 is resiliently held by the leafspring 370. Namely, during the alignment, two ray beams are interceptedby the intercepting plate 365 during aligning so that the window C₂ inthe mask 363 is not exposed to two ray beams. For conducting theexposure after the completion of aligning operation, the arm 366 towhich the intercepting plate 365 is fixed is rotated by means of thebobbin 372 so that the window C₂ in the mask 363 is exposed to two raybeams. After the exposure, the arm 366 is rotated manually and isresiliently pressed and held by the leaf spring 369.

A reference numeral 373 denotes a rotary ring to which the rotary plate364 is fixed, 374 denotes a rod for guiding the rotary ring, 375 denotesa rod support for supporting the rod 374 and 375 denotes a base to whichthe rod support is fixed. In order to prevent vibration from beingtransmitted to the vibration-free base E, the base 376 is fixed to a bed(not shown) different from the vibration-free base E. A referencenumeral 377 denotes a compression coiled spring disposed between the rodsupport 375 and the rotary ring 373 and adapted to act along the guideconstituted by the rod 370. A reference numeral 378 designates a nutscrewed to the threaded portion of the rod 370, while a numeral 379designates a guide pin fixed to the rod 374 and received by a groove373a formed in the rotary ring 373.

When the rotary ring 373 is within the range of between (a) and (b) ofthe groove 373a shown in FIG. 40, the rotary ring 373 is moved straightback and forth in the direction of z-axis while being guided by theguide pin 379, as the nut 378 is tightened or loosened. The straightmovement of the rotary ring 373 causes a straight movement of the rotaryplate 364 in the direction of the z-axis. The distance between the mask363 and the mask B is adjusted by the straight movement of the rotaryplate 364.

As the nut 378 is loosened to bring the rotary ring 373 relatively tothe guide pin 379 to the position (b) in the groove 373a, the rotaryring 373 can be rotated manually around the axis of the rod 374 in thedirection of the angle θ until the portion (c) of the groove 373 of therotary ring 373 contacts the guide pin 379. Then, as the nut 378 isfurther loosened, when the guide pin 379 is within the region of between(c) and (d) in the groove 373a in the rotary ring 373, the rotary ring373 moves in the direction of z-axis while being guided by the guide pin379.

In order to mount and demount the specimen W and the mask B on and fromthe specimen holder 320, the nut 374 is losened to the position (b) inthe groove 373a in the rotary ring 373 so that the rotary plate 364 donot hinder the mounting and demounting of the specimen W and the mask B.When the groove 373a of the rotary ring 373 is moved to the position(b), the rotary ring 373 is rotated manually until the portion (c) ofthe groove 373a is contacted by the guide pin 379 and, then, as the nut373 is further loosened, the rotary plate 364 connected to the rotaryring 372 is held at the position shown by one-dot-and-dash line (e).

After the mounting of the specimen W and the mask B, the nut 378 istightened until the position (c) in the groove 373a in the rotary ring373 is reached, and the rotary ring 373 is rotated until the portion (b)of the groove 373a in the rotary ring 373 is contacted by the guide pin379. Then, the nut 378 is tightened to move the rotary ring 373 straightto adjust the distance between the mask 363 and the mask B.

An explanation will be made hereinunder as to the optic path fullintercepting mechanism DA, with specific reference to FIGS 41 and 42.

A rotary lever 380 is fixed to a rotary solenoid 381 which in turn isfixed to a fixing plate 382. A rod 383 guided by a rod support 384 isconnected to the fixing plate 382. A reference numeral 385 designates anadjusting screw for effecting height adjustment of the rod 383 withrespect to the optic axis. The rod support 384 is fixed to a base 386which in turn is mounted on a base (not shown) different from thevibration-free base E. For passing the ray RA to the specimen W, therotary solenoid 381 is operated to bring the rotary lever 380 to theposition shown by one-dot-and-dash line (f₁).

Using the system as described hereinbefore, the exposure method of theinvention is carried out in the following steps (1) to (27).

(1) The laser source 310 is started to emit a coherent ray.

(2) The ray is intercepted by the optic path full intercepter DA.

(3) The specimen W is mounted on the specimen holder 320 and is held byvacuum sucking.

(4) The mask B is mounted on the specimen holder 320 so that the windowB₁ of the mask B is arranged to the position of the grid G on thespecimen W and is held by vacuum sucking.

(5) The optic path partial intercepter C is operated to bring the windowC₁ in the mask 363 thereof to the position corresponding to the windowB₁ in the mask B. Namely, the nut 378 is tightened until the rotary ring373 comes to the position (c₁) in the groove 373a, and the rotary ring369 is rotated until the portion (b₁) of the groove 373a is contacted bythe guide pin 379. Subsequently, the nut 378 is further loosened and therotary ring 373 is further moved straight until a predetermined distancebetween the mask 363 and the mask B is obtained. Then, the arm 366 isrotated to bring the intercepting plate 365 to the positioncorresponding to the window C₂ in the mask 363, so as to prevent thewindow C₂ from being exposed to the two ray beams. The arm 366 is thenheld in this position by the leaf spring 369.

(6) To dismiss the interception of the light by the optic pathfullintercepter DA to permit the ray beams to pass through.

(7) The coherent ray beam RA from the laser source 310 is applied to thebeam splitter BS through the reflecting mirrors 311, 312, lens 313, pinhole 314, collimeter lens 315 and reflecting mirror 316, and isamplitudesplitted by the beam splitter BS into a reflected ray beam R₁and transmitted ray beam R₂ which impinge upon the specimen W throughthe reflecting mirrors M₁, M₂ and the window C₁ in the mask 363 and thewindow B₁ in the mask B.

(8) The position of the specimen W is adjusted in the α direction and βdirection to minimize the number of the interference fringes formed bytwo ray beams impinging upon the specimen W. The correction of positionin the α direction is conducted by rotating the specimen holder 320 by asmall angle α around the x axis by the balance of tightening force ofthe bolt by which the specimen holder 320 is fixed to the rotarymechanism A₁ and the resilient force produced by the belleville spring322. The position correction in the β direction is conducted byoperating the β rotation mechanism A₂.

(9) An adjustment in the direction of z axis is conducted by the z-axisdrive mechanism A₃ so as to make the pitch of the grid G on the specimenW equal to the pitch of the interference fringe of two ray beams.

(10) Two ray beams impinging upon the grid G are diffracted by the gridG into rays R₃ and R₄ which are applied to the photodetectors D₁ and D₂through the optic systems including lenses L₁ and L₂, and the lightintensities, as positional information concerning the relative positionbetween the interference fringe of two ray beams and the grid G aredetected.

(11) The position of the specimen W is adjusted by the rotary adjustingmechanism A₁ and x-axis drive mechanism A₄ of the fine adjustingmechanism A so as to maximize the intensity of the detected ray beams.Namely, the rotary drive mechanism A₁ is operated to rotate the specimenW so as to maximize the ray intensity. Subsequently, the x-axis drivemechanism A₄ is controlled to drive the specimen W in the direction of xaxis to maximize the ray intensity. This two kinds of operation areconducted repeatedly to set the specimen W at the position where the rayintensity is maximized.

(12) The rays are intercepted again by the optic path full intercepterDA.

(13) The intercepting plate 365 and the arm 366 are rotated such thatthe window C₂ of the mask 363 in the optic path partial intercepter C isexposed to two ray beams.

(14) The interception of the rays by the optic path full intercepter DAis dismissed to permit the ray R to pass therethrough.

(15) The operation in the step (13) above permits two ray beams, i.e.the reflected beam R₁ and the transmitted ray beam R₂, to pass throughthe window C₂ in the mask 363 and the window B₂ in the mask B,respectively, so that these ray beams impinge upon the exposure positionon the specimen W thereby to effect the exposure.

(16) After the exposure, the ray beam is intercepted again by the opticpath full intercepter DA.

(17) The specimen W is moved by the x-axis drive mechanism A₄ to changethe exposure position of the specimen W, i.e. such that the window B₁ ofthe mask B corresponds to the position which corresponds to the windowC₁ of the mask 363.

(18) Two rays are intercepted so that the window C₂ of the mask 363 onthe optic path partial intercepter is not exposed to two ray beams.

(19) Steps (6) to (18) are repeated.

(20) The exposure is accomplished after exposing all portions of thespecimen W.

(21) Ray beams are intercepted by the optic path full intercepter DA.

(22) In order to prevent the optic path partial intercepter C fromhindering the mounting and demounting of the mask B and the specimen W,the following operation is conducted. Namely, the nut 378 is loosened tothe position (b) in the groove 373a in the rotary ring 373. When therotary ring 373a had reached the position (b), it is rotated until theportion (c) of the groove 373a contacts the guide pin 379. Then, the nut378 is further loosened so that the rotary plate 364 connected to therotary ring 373 is held at the position shown by one-dot-and-dash line(e).

(23) Holding of the mask B by vacuum sucking is dismissed so that themask B is mounted or demounted on or from the specimen holder 320.

(24) Holding of the specimen W by vacuum sucking is dismissed and thespecimen W is mounted on or demounted from the specimen holder 320.

(25) The next specimen W is mounted.

(26) Steps (4) to (20) are repeated.

(27) The exposure process is completed as all pieces of specimen areexposed through the steps explained hereinabove.

As has been described, in the exposure system of the describedembodiment, a ray beam RA emitted from a laser source 310 is made toimpinge through optic systems from two directions. The specimen W havinga grid G substantially parallel to the interference fringe of two raybeams is disposed in the optic paths of two ray beams. The raysreflected by the grid G are converged through the optic system and areled to photodetectors D₁ and D₂ which produce outputs representing thepositional relationship between the interference fringe of two rays andthe grid G. Then, the correction of position of the specimen W in the θand x directions is conducted by operating the θ rotary mechanism A₁ andthe x-axis drive mechanism A₄, thereby to permit an alignment with asub-micron order of precision. After aligning the grid G of the specimenW and the interference fringe of two ray beams with a high degree ofaccuracy, the intercepting plate 363 of the optic path partialintercepter C is rotated to expose the window C₂ of the mask 363 to tworay beams, so that two ray beams impinge upon the portion of thespecimen W to be exposed. It is, therefore, possible to form a minutepattern of sub-micron order within the atmospheric air. In addition, alarger through-put becomes obtainable because the patterns aretransferred at once by means of two ray beams.

The formation of the uniform fine pattern by two ray beams with the rayintensity distribution of the ray beam produced by the laser source 310is possible only within the range of between 20 Φ and 40 Φ mm. Due tothe presence of error such as those due to distortion of thesemiconductor substrate, superposing error and so forth, it is notpossible to expose a large specimen at once. Therefore, as shown in FIG.34, a plurality of blocks of grid G are formed at the portions, to beexposed, of the specimen W. With this arrangement, it is possible toexpose the specimen W for each block of the grid G, by employing a mask363 which is provided at it portion corresponding to one of the blockswith a window C₁ and a window C₂ at its portion corresponding to any oneof the portions, to be exposed, of the specimen W. It is thus possibleto effectively form fine patterns even on a large-size specimen W.

Since the lengths of the sizes of the windows B₁, B₂ in the mask B aresmaller than those of the windows C₁, C₂ or the mask 363 of the opticpath partial intercepter C, the diffraction of rays around the edges ofthe windows C₁, C₂ is prevented to avoid any noise which may, otherwise,be contained by the ray intensities detected by the photodetectors D₁and D₂ and, hence, to attain an alignment with a high degree ofprecision.

Usually, 0.5 to 1 hour is required until the coherent ray beam from thelaser source 310 is stabilized after the start up of the laser source310. In order to prevent accidental exposure to light which may impingeat the time of, for example, mounting or demounting of the specimen W,the optic path for the ray beam directed to the specimen is selectivelyintercepted fully by the optic path full intercepter DA. With thisarrangement, it is possible to obtain stable coherent ray beamcontinuously.

Furthermore, by providing the z-axis drive mechanism and the rotary αand β rotation mechanisms, it is possible to obtain greater differencebetween the maximum value and minimum value of the ray intensitydetected by the photodetectors D₁ and D₂, so that it becomes possible toobtain an alignment with a high degree of accuracy.

In order to realize the alignment as described hereinbefore, it isesential that the optic system itself is well aligned. An explanationwill be made hereinunder as to an example of the apparatus for attainingthis alignment.

As shown in FIG. 43, a diffraction grid G having a pitch P of, forexample, 1 μm is formed on the surface of the area of the specimen Wwhere the pattern is not to be formed, e.g. on the scribe line, suchthat the grid extend in parallel with the interference fringe formed asa result of mutual interference between two ray beams R₁, R₂. Thediffracted rays R₃ and R₄ from the diffraction grid G impinge upon thephotodetectors D₁ and D₂. The light of the reflected ray beam R isdiffracted by the diffraction grid G so that a plurality of diffractedray beams are formed. The area counter-clockwise from the direction ofmovement of the diffracted ray beam is considered as being of plus (+).As will be seen from FIG. 44, among the diffracted ray beams, thediffracted ray R₁₀ of 0 (zero) order and the diffracted ray R₁₁ of -1order are reflected by reflecting mirrors M₂ and M₁ and come back to thelaser source through a two rays split optic system 417, reflectingmirror 416 and the parallel optic system 425, as will be best seen fromFIG. 49. Similarly, the light of the transmitted ray R₂ is diffracted bythe diffraction grid G on the specimen into a plurality of diffractedrays. Among the plurality of diffracted rays, the diffracted ray beamR₂₀ of 0 (zero) order and the diffracted ray beam R₂₁ of +1 order arereflected by reflecting mirrors M₁ and M₂ and return to the laser sourcethrough the two ray beam splitting optic system 417, reflecting mirror416 and the parallel optic system 415.

A reference numeral 418 denotes a light-receiving element for detectingthe positions of returning lights of respective diffracted ray beamsR₁₀, R₁₁, R₂₀, R₂₁. The light-receiving element 418 is disposed in thevicinity of the pin hole 414 and is composed of four separatelight-receiving portions a, b, c and d, and the received lights in theform of electric signals are derived through respective lead lines a',b', c' and d'. A hole e for passing the ray beam R which has passedthrough the pin hole 414 is formed in the center of the light receivingelement 418. The hole e is located on the optic axis.

In order to permit adjustment of angles Φ₁ and Φ₂ of the reflectingmirrors M₁ and M₂, these mirrors M₁ and M₂ are provided with means forrotating these mirrors in the α and β directions around the x axis and yaxis, respectively, by representing the optic axis by z as shown inFIGS. 47 and 48. More specifically, a reference numeral 419 designates amovable frame for fixing the reflecting mirror 420 denotes a supportplate having a projection 420-α and 421, 422 denote micrometer headsfixed to the movable frame 419. The arrangement is such that, as themicrometer heads 421, 422 are operated, the ends 421-a, 422-a of thesemicrometer heads push the support plate 420 so that the reflectingmirror is rotated in the α and β directions around the pivot constitutedby the projection 420-a of the supporting plate 420, against the tensileforces produced by the tensile springs 423, 424.

Representing the wavelength of the laser beam by λ and the pitch of thediffraction grid G on the wafer W by P, the diffraction angle Φ_(d1) atwhich the reflected ray R₁ is diffracted by the diffraction grid G isrepresented as follows by the Bragg condition.

    P(sin Φ.sub.d1 -sin Φ.sub.1)=mλ             (4)

where, m being 0, 1, 2, 3 and other positive integers.

In the case of m=0, i.e. the diffracted ray beam R₁₀ of 0 order, thediffraction angle Φ_(d10) is given by the following equation (5).

    P(sin Φ.sub.d10 -sin Φ.sub.1)=0                    (5)

Thus, in this case, a condition of Φ₁₀ =Φ₁ is obtained. Namely, thediffraction angle of the diffracted ray R₁₀ of 0 degree equals to theangle Φ₁ of incidence of the reflected ray R₁, so that the diffractedlight ray beam is returned to the laser source through the reflectingmirror M₂, two ray splitting optic system 417, reflecting mirror 416 andthe parallel optic system 415.

When m=1, i.e. in the case of the diffracted ray R₁₁ of the 1st order,the diffraction angle Φ_(d11) is given as follows.

    P(sin Φ.sub.d11 -sin Φ.sub.1)=λ             (6)

If the condition of Φ₁ =-Φ_(d11) is met, the following condition isobtained. ##EQU5##

The diffraction angle Φ_(d2) at which the transmitted ray beam R₂ isdiffracted by the diffraction grid G is derived from the Bragg conditionas follows.

    P(sin Φ.sub.d2 -sin Φ.sub.2)=mλ             (8)

where, m is 0, 1, 2, 3 . . . and other positive integers.

In the case of m=0, i.e. the diffracted ray R₂₀ of 0 order, thediffraction angle Φ_(d20) is given by the following equation.

    P(sin Φ.sub.d20 -sin Φ.sub.2)=0                    (9)

Thus, the condition of Φ_(d20) =Φ₁ is met. Thus, the diffraction angleΦ_(d20) of the diffracted ray R₂₀ of 0 (zero) order equals to the angleΦ₂ of incidence of the transmitted ray R₂ so that the diffracted ray R₂₀is returned to the laser source through the reflecting mirrors M₁, tworay beam splitting optic system 417, reflecting mirror 416 and paralleloptic system 415.

In the case of m=1, i.e. in the case of the diffracted ray R₂₁ of the1st order, the diffraction angle Φ_(d21) is given by the followingformula.

    P(sin Φ.sub.d21 -sin Φ.sub.2)=λ             (10)

If the condition of Φ_(d21) =-Φ₂ is met, the following relationship isestablished. ##EQU6##

If the conditions of Φ₁ ≠(-Φ₂), Φ₁ ≠(-Φ_(d1)) and Φ₂ ≠(-Φ_(d21)) are metas shown in FIG. 49, the diffracted rays R₁₀, R₁₁, R₂₀ and R₂₁ afterpassing through the parallel optic system 415 do not pass through thehole e of the light receiving element 418 but impinge upon any one ofthe light-receiving portions a, b, c and d of the light receivingelement 418. The intensities of ray beams received by respectivelight-receiving portions are converted into electric signals and aretaken out as position information. Then, by suitably operating therotary drive mechanisms for the reflecting mirrors M₁ and M₂, it ispossible to realize the state in which none of the light-receivingportions a, b, c and d receive the diffracted ray, i.e. the state inwhich all of the diffracted rays pass through the hole e in thelight-receiving element 417. This state is expressed by the followingequation (12).

    Φ.sub.1 ≈(-Φ.sub.2)≈(-Φ.sub.d1)≈(+Φ.sub.d21) (12)

Representing the pitch of the interference fringe formed by interferencebetween the reflected ray R₁ and the transmitted ray R₂ by Λ, this pitchis determined as follows. ##EQU7##

The equation (13) is transformed as follows by a substitution of theequation (12). ##EQU8##

The equation (14) is further transformed as follows, using the equation(7). ##EQU9##

It is thus possible to obtain the pitch Λ of the interference fringe oftwo ray beams R₁ and R₂ substantially equal to the pitch P of thediffraction grid G on the specimen W.

As the pitch Λ of the interference fringe of two rays is madesubstantially equal to the pitch P of the diffraction grid G of thespecimen, the diffraction grid G emits the ray beams R₃, R₄ which areformed as a result of the wave-surface splitting of the interferencelight of two ray beams R₁ and R₂, the splitting being made by thediffraction grid G. As a result, ray intensities which represent thepositional relationship between the interference fringe of two ray beamsand the grid at a high resolution can be obtained by photodetectors D₁and D₂. Using these light intensities representing the positionalrelationships, it is possible to detect the positional relationshipbetween the interference fringe of two ray beams and the specimen W, andthe position of the specimen W, i.e. position of the same in thedirection perpendicular to the interference fringe and rotation of thesame around optic axis is corrected in accordance with the thus detectedpositional relationship, thereby to align the interference fringe of tworay beams R₁ and R₂ with the specimen W.

More specifically, by using an He-Cd laser beam of a wavelength of 4416Å, it is possible to form interference fringe of a small pitch of 1 μm.Using this interference fringe in combination with a diffraction grid Gof 1 μm pitch, it is possible to align the specimen such as asemiconductor wafer with the interference fringe at a high degree ofaccuracy of not greater than several hundreds of Å.

Thereafter, an exposure is made by exposing the portion of the specimenW, i.e. the semiconductor wafer, on which the pattern is to be formed.This pattern exposure can be conducted accurately by using, incombination with the aligning system of the invention explainedhereinbefore, an exposure system having an exposing function whichcarries out the exposure method of the invention making use ofinterference of two laser beams. The exposure for forming fine patternsafter the alignment may be conducted by a known exposure system such asa projection exposure system.

Although the light receiving system 418 used in the described embodimenthas four separate light-receiving portions, the same effect can beproduced by the use of a light-receiving element unit having fourlight-receiving elements fixed to a substrate made of a material whichpermits an easy formation of the central hole for passing ray beams.

In another modification, a light-receiving element, disposed in thevicinity of the pin hole 44, has light-receiving surfaces for receivingdiffracted rays R₁₀, R₁₁, R₂₀ and R₂₁ arranged in a matrix-like form andprovided at the center with a fine aperture for passing the ray beams.According to this arrangement, it is possible to obtain the positions towhich the diffracted ray beams are returned as the position informationof second order and, hence, to facilitate the coincidence of the pitchof the interference fringe with the pitch P of the diffraction grid G.

In a further modification, the light-receiving element 418 is disposedin the vicinity of the focal point of the diffraction optic system 413,so that the diffracted rays R₁₀, R₁₁, R₂₀, R₂₁ are returned to thelight-receiving surface of the light-receiving element 418 in the mostconstricted state. With this arrangement, therefore, it is possible tomake the pitch of the interference fringe coincide with the pitch P ofthe diffraction grid G accurately. By disposing the pin hole 414 and thelight-receiving element 418 in the vicinity of the focal point of thediffusion optic system 413, it is possible to align the pitch of theinterference fringe with the pitch P of the diffraction grid G highlyaccurately, while intercepting unnecessary diffracted ray portions.

As will be understood from the foregoing description, the presentinvention offers the following advantages.

According to the invention, interference fringe is formed by allowingtwo mutually conjugate ray beams to interfere with each other, andaligned with a grid formed on a wafer. The rays formed as a result ofwave-surface splitting by the grid, i.e. the ray beam reflected by thegrid and the ray beam transmitted by the grid are made to interfere witheach other through a lens and the intensity of the interfered ray beamis measured. It is possible to know the positional relationship betweenthe interference fringe and the grid by the measurement of the rayintensity, so that a highly accurate alignment can be attainable throughthis measurement. A high degree of accuracy of alignment is attainableby measuring the intensities of the sum and difference of diffracted raybeams from conjugate grids. By applying this technic to an exposureprocess employing laser holography, it is possible to effect thealignment and exposure, simultaneously without using any mask.

According to another feature of the invention, the interference fringeis made to align with a grid having a pitch which is n (n being aninteger) times as large as the pitch of the interference fringe, and theray beams formed by wave-surface splitting, i.e. reflection andtransmission by the grid, are made to interfere again with each otherand the intensity of the interferred ray beam is measured. Through thismeasurement of the ray intensity, it is possible to know the relativeposition between the interference fringe of two ray beams and the grid,so that a highly accurate alignment becomes attainable. By applying thistechnique to the exposure process employing laser holography, it ispossible to effect the alignment and the exposure simultaneously withoutusing any mask. The accuracy of the alignment in this case is on theorder of several hundreds of Å when the pitch of the grid on the waferis 1 μm.

In a practical form of the aligning method of the invention, the raybeams diffracted from the grid formed on a reticle is applied to a gridformed on a wafer, and the intensities of ray beam diffracted by thegrid on the wafer are measured. By so doing, it is possible to align thepattern on the wafer with the reticle with a high degree of accuracy.Furthermore, it is possible to effect the alignment in a short period oftime by making use of a figure pattern provided on the reticle or thewafer. A high degree of accuracy of alignment on the order of severalhundreds of Å can be obtained when the pitch of the grid on the wafer is1 μm. Although in the description of the embodiments the reticle and thewafer are assumed to be a first substrate and a second substrate, thisembodiment can equally be applied to alignment of ordinary photo maskother than the reticle, with the wafer or even to alignment of ordinarytwo objects which are to aligned with each other. Although in thedescribed embodiment the rays transmitted through the reticle is used,the invention can equally be carried out by making use of the raysreflected by the reticle.

According to an embodiment of the invention, the accuracy of detectionby the photodetector can be enhanced by the following arrangement. Usingthe interference fringe formed as a result of interference between tworay beams and a grid, the rays reflected and transmitted by the grid areled to the photodetectors through slits which are disposed with theirlonger sides extending in parallel with the interference fringe, and theintensities of these ray beams are measured by the photodetectors. By sodoing, it is possible to detect the degree of parallelness between theinterference fringe of two ray beams and the grid, as well as relativeposition therebetween in the direction of the pitch, so that thealignment can be achieved at a specifically high accuracy on the orderof less than 0.05 μm.

Furthermore, according to a further feature of the invention,interference fringe formed as a result of interference between mutuallyconjugate ray beams is aligned with a grid formed on a wafer, the gridhaving a pitch equal to or n (n being an integer) times as large as thepitch of the interference fringe. After completing this aligningoperation, an exposure is conducted using the same system as that usedfor the alignment. This arrangement simplifies the system advantageouslybecause the exposure is conducted by the same ray beam source as thatused in the alignment, while ensuring the high degree of accuracy of thealignment inherent to the invention.

The invention permits a high degree of accuracy of alignment for formingfine pattern, even when the exposure is made by X-ray ion beams,ultraviolet rays and so forth.

In a further form of the invention, a diffraction grid on a specimen ispositioned substantially in parallel with an interference fringe, and aplurality of diffracted ray beam diffracted by the diffraction grid arereceived by light-receiving elements which produce as their outputs thepositional information. Then, by rotating, for example, two reflectingmirrors, the incidence angles of two ray beams to the diffraction gridare adjusted until the pitch of the interference fringe of two ray beamsbecome substantially equal to the pitch of the diffraction grid. Withthis arrangement, it is possible to detect the relative position betweenthe interference fringe of two ray beams and the specimen at a highaccuracy of an order of less than several hundreds of Å. It is,therefore, possible to obtain an exposure system which can permits, inspite of the simplified construction, the formation of fine patterns ofsub-micron order and at a large through-put, with a simple construction.

What is claimed is:
 1. An aligning method comprising.[.:.]. the stepsof.Iadd.: .Iaddend.applying coherent ray beams from two directions toform .Iadd.an .Iaddend.interference fringe through interference of saidcoherent ray beams; disposing a grid in the paths of said ray beamssubstantially in parallel with said interference fringe; allowing theray beams .Iadd.either .Iaddend.reflected .[.and.]. .Iadd.or.Iaddend.transmitted by said grid to interfere again through an opticsystem and leading the interfered ray beam to photodetecting means;detecting the relative .[.position.]. .Iadd.positions .Iaddend.betweensaid interference fringe of said two ray beams and said grid throughmeasuring the intensity of said interfered ray beam by saidphotodetecting means; and aligning said interference fringe and saidgrid with each other in accordance with the result of the measurement.2. An aligning method according to claim 1, wherein said coherent raybeams have an equal wavelength.
 3. An aligning method according to claim1, comprising the step of detecting the diffracted ray reflected ortransmitted by said grid.
 4. An aligning method according to claim 1,wherein at .[.lest.]. .Iadd.least .Iaddend.two photodetectors areprovided .Iadd.as said photodetecting means.Iaddend..
 5. An aligningmethod according to claim 4, wherein said photodetectors operateindependently.
 6. An aligning method according to claim 4, wherein saidphotodetecting means are adapted to detect mutually conjugate diffractedrays.
 7. An aligning method according to claim 6, wherein the sum ordifference of the outputs of said photodetecting means is used for thedetection of the position.
 8. An aligning method according to claim 1,wherein said photodetecting means is disposed on the focal point of anoptic system which converges the ray beams diffracted by said grid. 9.An aligning method comprising: applying coherent ray beams from twodirections to form .[.interferent.]. .Iadd.an interference.Iaddend.fringe through interference of said coherent ray.[.beam.]..Iadd.beams.Iaddend., disposing a grid in the paths of saidray beams substantially in parallel with said interference fringe;allowing the ray beam .Iadd.either .Iaddend.reflected and transmitted bysaid grid to interfere again through an optic system and leading theinterfered ray beam to photodetecting means; changing the relativeposition between the interference fringe of two ray beams and said grid;detecting the amount of change of the relative position; and detectingthe position by comparing the intensity of .Iadd.the interfered.Iaddend.ray beam measured by said photodetecting means with the amountof change of the relative position.
 10. An aligning method according toclaim 9, wherein the position is detected by comparing the maximumand/or the minimum values of the ray intensity as measured by saidphotodetecting means with the deviation of said interference fringe andsaid grid.
 11. An aligning method comprising: applying coherent raybeams from two directions to form .Iadd.an .Iaddend.interference fringethrough interference of said coherent .[.rays.]. .Iadd.raybeams.Iaddend., disposing a grid in the paths of said ray beamssubstantially in parallel with said interference fringe, said having apitch which is n (n being an integer) times as large as the pitch ofsaid interference fringe; leading the ray beams reflected or transmittedby said grid to photodetecting means; detecting the relative positionbetween said interference fringe of said two ray beams and said gridthrough measuring the intensity of said ray beam reflected ortransmitted by said grid by said photodetecting means; and aligning saidgrid with said interference fringe in accordance with the result of themeasurement.
 12. An aligning method according to claim 11, wherein agrid having a pitch which is n (n being an integer) times as large asthe pitch of said interference fringe is formed by a photolithographictechnique.
 13. An aligning method according to claim 11, wherein a gridhaving a pitch which is n (n being an integer) times as large as thepitch of said interference fringe is formed by a.[.photolithographyic.]. .Iadd.photolithographic .Iaddend.technique, andwherein a pattern beforehand positioned in relation to said grid isaligned with said interference fringe.
 14. An aligning method accordingto claim 13, wherein a figure pattern of a period different from that ofsaid grid is formed and, after making an approximate alignment usingthis figure pattern, said alignment of said grid and said interferencefringe is conducted.
 15. An aligning method comprising: applying acoherent first ray beam into .Iadd.a .Iaddend.first one of twosubstrates to be aligned with each other, said first one of .Iadd.the.Iaddend.substrates receiving said first coherent ray beam beingprovided on its surface with two first diffraction grids; applyingsecond and third ray beams diffracted by .Iadd.the .Iaddend.respectivediffraction grids into the second one of the substrates; leading afourth ray beam reflected or transmitted by a second diffraction grid onthe surface of said second substrate to a photodetecting means andmeasuring the intensity of said fourth ray beam by said photodetectingmeans thereby to detect the relative position between the interferencefringe of two ray beams applied to said second substrate and said seconddiffraction grid on said second substrate; and aligning said firstsubstrate and said second substrate with each other using the detectedrelative position between said interference fringe and said seconddiffraction grid.
 16. An aligning method according to claim 15, whereina figure pattern of a period different from that of said second grid isformed in a part of said second grid on said second substrate and anapproximate alignment is made using said figure pattern.
 17. An aligningmethod according to claim 15, wherein, in parts of the regular firstdiffraction grids on said first substrate, .Iadd.there are.Iaddend.formed .[.are.]. figure patterns of a period different from theperiods of said first grids, said figure patterns being arranged insymmetry with respect to said first grids; the method comprising:applying two ray beams diffracted by respective first diffraction gridsto said second diffraction grid on said second substrate; and effectingan approximate alignment using said figure pattern contained by the raybeam after diffraction by said second diffraction grid.
 18. An aligningmethod comprising.[.:.]. the steps of.Iadd.: .Iaddend.applying acoherent first ray beam into .Iadd.a .Iaddend.first one of twosubstrates to be aligned with each other, said first one of .Iadd.the.Iaddend.substrates receiving said first coherent ray beam beingprovided on its surface with a first diffraction grid; applying a secondray beam diffracted by said first diffraction grid into the second oneof the substrates; applying a reference third ray beam interferable withsaid second ray beam to the second substrate; leading a fourth ray beam,which is formed by reflecting or transmitting said second and third raybeams by a second diffraction grid on said second substrate, to aphotodetecting means and measuring the intensity of said fourth ray beamby said photodetecting means thereby to detect the relative positionbetween the interference fringe of said second and third ray beamsapplied to said second substrate and said second diffraction grid onsaid second substrate; and aligning said first substrate and said secondsubstrate with each other using the detected relative position betweensaid interference fringe and said second diffraction grid.
 19. Analigning method according to claim 18, wherein a figure pattern of aperiod different from that of said second grid is formed in a part ofsaid second grid on said second substrate and an approximate alignmentis made using said figure pattern.
 20. An aligning method comprising:applying coherent ray beams from two directions to form .Iadd.an.Iaddend.interference fringe by the mutual interference of the two raybeams; placing a grid in the optic paths of said two ray beams; leadingthe ray reflected or .[.diffracted.]. .Iadd.transmitted .Iaddend.by saidgrid to a photo-detecting means through a slit to measure the intensityof said ray thereby to detect the relative position between saidinterference fringe and said grid; and aligning said interference fringewith said grid.
 21. An aligning method according to claim 20, whereinsaid slit is disposed such that the longitudinal side of said slitextends substantially in parallel with said interference fringe of saidtwo ray beams.
 22. An aligning method according to claim 20, whereinsaid slit includes a first slit disposed with its longitudinal sideextended substantially in parallel with said interference fringe of saidtwo ray beams, a second slit inclined at a predetermined angle β₁ tosaid first slit and a third slit inclined at another predetermined angleβ₂ to said first slit, the ray beams having passed through said threeslits being introduced to respective photodetecting means for measuringintensities of .Iadd.the .Iaddend.ray beams so that the direction ofinclination of said grid with respect to said interference fringe of two.Iadd.of said .Iaddend.ray beams is detected to permit the alignment ofsaid interference fringe and said grid with each other.
 23. An aligningmethod according to claim 20, wherein said grid is disposed in thevicinity of the point of intersection of scribe lines of an IC wafer, at45° inclination to the scribe lines.
 24. An aligning and exposing methodcomprising: applying coherent first radiant ray beams having a firstwavelength from two directions; placing a grid disposed in the opticpaths of said first radiant ray beams substantially in parallel with theinterference fringe formed by mutual interference of two first radiantray beams; allowing the ray beams .Iadd.either .Iaddend.reflected.[.and.]. .Iadd.or .Iaddend.transmitted by said grid to interfere againand leading the interfered ray beam to a photo-detecting means for themeasurement of intensity of .[.said.]. .Iadd.the interfered .Iaddend.raybeam; aligning said interference fringe of .Iadd.the .Iaddend.two firstradiant ray beams and said grid thereby to align a pattern formed on thesame substrate as said grid; and effecting an exposure with a secondradiant ray beam.
 25. An aligning and exposing method according to claim24, wherein said first radiant ray beam and said second radiant ray beam.[.has an.]. .Iadd.have .Iaddend.equal.[.wavelength.]..Iadd.wavelengths.Iaddend..
 26. An aligning and exposingmethod according to claim 25, wherein said first radiant ray beam andsaid second radiant ray beam have different wavelengths.
 27. An exposuremethod comprising: disposing a light-receiving element in the vicinityof a coherent ray beam; preparing an optic system capable of effectingan amplitude splitting of said ray beam and superposing the split raycomponents to make them interfere with each other; forming aninterference fringe in a space by allowing two ray beams formed by theamplitude-splitting to interfere with each other; placing a diffractiongrid in the optic paths of said two ray beams substantially in parallelwith said interference fringe; returning the ray beams diffracted bysaid diffraction grid through said optic system; measuring theintensities of the returned ray beams by said light-receiving element;making an adjustment to substantially equalize the pitch of saidinterference fringe to the pitch of said diffraction grid by making useof the result of the measurement, thereby to align said interferencefringe and said grid with each other; and exposing said interferencefringe.
 28. An exposure method comprising: allowing a coherent ray beamto pass through a diffusion optic system for diffusing said coherent raybeam; disposing a pin hole in the vicinity of the point where said raybeam is constricted by said diffusion optic system; disposing alight-receiving element in the vicinity of the ray beam which has passedthrough said pin hole; placing an optic system capable of making anamplitude splitting of said ray beam and superposing the ray beamsformed by the splitting to make them interfere with each other; forming.[.the.]. .Iadd.an .Iaddend.interference fringe in a space by allowingthe rays formed by splitting to interfere with each other; disposing adiffraction grid in the optic paths of said ray beams formed bysplitting substantially in parallel with said interference fringe;returning the ray beams diffracted by said diffraction grid through saidoptic system; measuring the intensities of the returned ray beams bysaid light-receiving element; effecting an adjustment to substantiallyequalize the pitch of said interference fringe with the pitch of saiddiffraction grid, aligning said grid with said interference fringe; andeffecting an exposure. .Iadd.29. An aligning method, comprising thesteps of applying coherent ray beams from two directions to form aninterference fringe through interference of said coherent ray beams;disposing a grid in the paths of said ray beams substantially inparallel with said interference fringe; allowing the ray beams eitherreflected or transmitted by said grid to interfere again through anoptic system and leading the interfered ray beam to photodetectingmeans; detecting the relative positions between said interference fringeof said two ray beams and said grid in accordance with a change in theoutput of said photo detecting means; and aligning said interferencefringe and said grid with each other in accordance with the result ofthe measurement. .Iaddend. .Iadd.30. A method of aligning a reticle anda wafer provided with a grid, said grid being set on a wafer which isoptically exposed through said reticle so as to be aligned with thelatter, comprising the steps of applying coherent ray beams from twodirections to form an interference fringe through interference of saidcoherent ray beams; disposing a grid in the paths of said ray beamssubstantially in parallel with said interference fringe; allowing theray beams either reflected or transmitted by said grid to interfereagain through an optic system and leading the interfered ray beam tophotodetecting means; detecting the relative positions between saidinterference fringe of said two ray beams and said grid in accordancewith a change in the output of said photodetecting means; and aligningsaid reticle and said wafer with each other in accordance with theresult of the measurement. .Iaddend.